Data commit

Task/Stable-marriage-problem/Ruby/stable-marriage-problem.rb

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+class Person
+  def initialize(name)
+    @name = name
+    @fiance = nil
+    @preferences = []
+    @proposals = []
+  end
+  attr_reader :name, :proposals
+  attr_accessor :fiance, :preferences
+
+  def to_s
+    @name
+  end
+
+  def free
+    @fiance = nil
+  end
+
+  def single?
+    @fiance == nil
+  end
+
+  def engage(person)
+    self.fiance = person
+    person.fiance = self
+  end
+
+  def better_choice?(person)
+    @preferences.index(person) < @preferences.index(@fiance)
+  end
+
+  def propose_to(person)
+    puts "#{self} proposes to #{person}" if $DEBUG
+    @proposals << person
+    person.respond_to_proposal_from(self)
+  end
+
+  def respond_to_proposal_from(person)
+    if single?
+      puts "#{self} accepts proposal from #{person}" if $DEBUG
+      engage(person)
+    elsif better_choice?(person)
+      puts "#{self} dumps #{@fiance} for #{person}" if $DEBUG
+      @fiance.free
+      engage(person)
+    else
+      puts "#{self} rejects proposal from #{person}" if $DEBUG
+    end
+  end
+end
+
+########################################################################
+# initialize data
+
+prefs = {
+  'abe'  => %w[abi eve cath ivy jan dee fay bea hope gay],
+  'bob'  => %w[cath hope abi dee eve fay bea jan ivy gay],
+  'col'  => %w[hope eve abi dee bea fay ivy gay cath jan],
+  'dan'  => %w[ivy fay dee gay hope eve jan bea cath abi],
+  'ed'   => %w[jan dee bea cath fay eve abi ivy hope gay],
+  'fred' => %w[bea abi dee gay eve ivy cath jan hope fay],
+  'gav'  => %w[gay eve ivy bea cath abi dee hope jan fay],
+  'hal'  => %w[abi eve hope fay ivy cath jan bea gay dee],
+  'ian'  => %w[hope cath dee gay bea abi fay ivy jan eve],
+  'jon'  => %w[abi fay jan gay eve bea dee cath ivy hope],
+  'abi'  => %w[bob fred jon gav ian abe dan ed col hal],
+  'bea'  => %w[bob abe col fred gav dan ian ed jon hal],
+  'cath' => %w[fred bob ed gav hal col ian abe dan jon],
+  'dee'  => %w[fred jon col abe ian hal gav dan bob ed],
+  'eve'  => %w[jon hal fred dan abe gav col ed ian bob],
+  'fay'  => %w[bob abe ed ian jon dan fred gav col hal],
+  'gay'  => %w[jon gav hal fred bob abe col ed dan ian],
+  'hope' => %w[gav jon bob abe ian dan hal ed col fred],
+  'ivy'  => %w[ian col hal gav fred bob abe ed jon dan],
+  'jan'  => %w[ed hal gav abe bob jon col ian fred dan],
+}
+
+@men = Hash[
+  %w[abe bob col dan ed fred gav hal ian jon].collect do |name|
+    [name, Person.new(name)]
+  end
+]
+
+@women = Hash[
+  %w[abi bea cath dee eve fay gay hope ivy jan].collect do |name|
+    [name, Person.new(name)]
+  end
+]
+
+@men.each {|name, man| man.preferences = @women.values_at(*prefs[name])}
+@women.each {|name, woman| woman.preferences = @men.values_at(*prefs[name])}
+
+########################################################################
+# perform the matching
+
+def match_couples(men, women)
+  men.each_value {|man| man.free}
+  women.each_value {|woman| woman.free}
+
+  while m = men.values.find {|man| man.single?} do
+    puts "considering single man #{m}" if $DEBUG
+    w = m.preferences.find {|woman| not m.proposals.include?(woman)}
+    m.propose_to(w)
+  end
+end
+
+match_couples @men, @women
+
+@men.each_value.collect {|man| puts "#{man} + #{man.fiance}"}
+
+########################################################################
+# check for stability
+
+class Person
+  def more_preferable_people
+    ( @preferences.partition {|p| better_choice?(p)} ).first
+  end
+end
+
+require 'set'
+
+def stability(men)
+  unstable = Set.new
+  men.each_value do |man|
+    woman = man.fiance
+    puts "considering #{man} and #{woman}" if $DEBUG
+
+    man.more_preferable_people.each do |other_woman|
+      if other_woman.more_preferable_people.include?(man)
+        puts "an unstable pairing: #{man} and #{other_woman}" if $DEBUG
+        unstable << [man, other_woman]
+      end
+    end
+    woman.more_preferable_people.each do |other_man|
+      if other_man.more_preferable_people.include?(woman)
+        puts "an unstable pairing: #{woman} and #{other_man}" if $DEBUG
+        unstable << [other_man, woman]
+      end
+    end
+  end
+
+  if unstable.empty?
+    puts "these couples are stable"
+  else
+    puts "uh oh"
+    unstable.each do |a,b|
+      puts "#{a} is engaged to #{a.fiance} but would prefer #{b}, and #{b} is engaged to #{b.fiance} but would prefer #{a}"
+    end
+  end
+end
+
+stability @men
+
+########################################################################
+# perturb
+
+puts "\nwhat if abe and bob swap..."
+
+def swap(m1, m2)
+  w1 = m1.fiance
+  w2 = m2.fiance
+  m1.fiance = w2
+  w1.fiance = m2
+  m2.fiance = w1
+  w2.fiance = m1
+end
+
+swap *@men.values_at('abe','bob')
+
+@men.each_value.collect {|man| puts "#{man} + #{man.fiance}"}
+stability @men